Vehicle steering control system including corrections for map position and detected obstacles

ABSTRACT

An azimuth change quantity θ of a road during traveling of a vehicle for a time δt is calculated based on road data provided by a navigation system and a vehicle speed provided by a vehicle speed sensor (at step S3 in FIG. 2). On the other hand, an azimuth change quantity Θ of the vehicle is calculated by integrating a yaw rate γ obtained from a yaw rate sensor over the time δt (at step S5). A deviation D between the azimuth change quantity θ of the road and the azimuth change quantity Θ of the vehicle is calculated (at step S6). When the deviation D becomes equal to or larger than a reference value β, it is determined that there is a possibility that the vehicle will depart from the road (at step S9) , and a predetermined steering torque is applied to a steering device, so that the deviation is converged into zero (at steps S10 and S11).

This is a divisional application of prior pending application U.S. Ser.No. 08/620,193, filed Mar. 22, 1996.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicle control system for performinga steerage control based on an azimuth change quantity of a roadcalculated from map information and a position of a subject vehicle.

2. Description of the Related Art

There is a technique conventionally known from Japanese PatentApplication Laid-open No.89298/85, which determines whether the subjectvehicle can pass through a curve existing ahead of the subject vehiclein a traveling direction at a current vehicle speed, by estimating aradius of curvature of the curve based on map data obtained by anavigation system, and gives a warning to a driver, when it isdetermined that the subject vehicle cannot pass through the curve.

In the above known technique, however, it is only determined whether thevehicle can pass through the curve at the current vehicle speed, and amisalignment of the vehicle from the curvature of the road is notdetected, resulting in a problem that a proper warning is difficult.Moreover, even if a warning is given when the driver has a lowereddriving capability due to a fatigue or when the driver is inattentivelydriving the vehicle, a driver's quick steering or braking operation isrequired to avoid the departing of the vehicle from the road, and anunskilled driver cannot cope with such operation, resulting in apossibility that the vehicle will depart from the road.

There are conventionally proposed various follow-up travel controlsystems which are designed to detect a vehicle traveling ahead of asubject vehicle (which will be referred to as an ahead-traveling vehiclehereinafter) by radar or the like and perform a vehicle-vehicle distancecontrol so that a distance between the subject vehicle from theahead-traveling vehicle is maintained constant. However, if a controlfor preventing the departing of the vehicle from the road and afollow-up travel control for permitting the vehicle to travel whilefollowing the ahead-traveling vehicle are conducted simultaneously, forexample, if a steerage control started when the driver is conducting thesteerage to cause the subject vehicle to trace a travel locus of theahead-traveling vehicle during the follow-up travel control, it isconsidered that the driver feels a sense of incompatibility. If thearrangement is such that both of the controls are switched from one toanother at each time by a manual operation, for example, when the driverhas lost sight of the ahead-traveling vehicle during the follow-uptravel control, the following problems are encountered: the driver mayforget the switching-over to the control for preventing the departing ofthe subject vehicle from the road, and such switching-over istroublesome for the driver.

There is also a technique known from Japanese Patent ApplicationLaid-open No.5-113822, which detects an obstacle existing ahead of thesubject vehicle on a travel road by a video camera or radar, andconducts a vehicle speed control or a steerage control to avoid thecollision of the subject vehicle against the obstacle, when it isdetermined that there is a possibility of the collision of the vehicleagainst the obstacle.

If the obstacle-avoiding control system is combined with the steeragecontrol system designed to determine whether there is a possibility ofthe departing of the vehicle from the road, based on the traveling stateof the vehicle and the shape of a road district existing ahead of asubject-vehicle position on a travel road, and to apply a steeringtorque to a steering means, when it is determined that there is thepossibility of the departing of the vehicle from the road, therebypreventing the departing of the vehicle from the road, the followingproblem is encountered: both of the controls interfere with each otherto make it difficult to perform a smooth avoidance of the obstacle.

Specifically, when the driver conducts the steerage to avoid theobstacle, the vehicle departs from an intrinsic course and hence, thesteerage control system applies a steering torque to the steering meansto return the vehicle to the original course. However, this steeringtorque is in a direction opposite from a direction of a steering torqueapplied by the driver to avoid the obstacle, and hence, there is apossibility that the burden of the driver's obstacle-avoiding operationis increased and that a sense of incompatibility is imparted.

SUMMARY OF THE INVENTION

Accordingly, it is a first object of the present invention to subjectthe steering device to a steerage control to reliably avoid thedeparting of the vehicle from the road.

It is a second object of the present invention to reconcile both of thecontrol for preventing the departing of the vehicle from the road andthe follow-up travel control for allowing the vehicle to travel whilefollowing the ahead-traveling vehicle.

It is a third object of the present invention to allow the driver toeasily perform an obstacle-avoiding operation while conducting thesteerage control for preventing the departing of the vehicle from theroad.

To achieve the above first object, according to the present invention,there is provided a vehicle control system comprising: a map informationoutputting means for outputting map information including a road onwhich a subject vehicle travels; a subject-vehicle position detectingmeans for detecting a subject-vehicle position on a map; a steeringmeans for steering a steering control wheel of the vehicle; asteering-torque applying means for applying a steering torque to thesteering means; and a control means for determining a deviation betweenan azimuth change quantity of the road on which the vehicle is travelingand an azimuth change quantity of the vehicle, and for driving thesteering-toque applying means such as to decrease the deviation.

With such arrangement, the deviation between an azimuth change quantityof the road on which the vehicle is traveling and an azimuth changequantity of the vehicle, is determined, and the steering torque isapplied to the steering means in the direction to decrease thedeviation. Therefore, even when the driver has a lowered drivingcapability, the possibility of the departing of the vehicle from theroad can be reduced remarkably.

To achieve the first object, according to the present invention, thereis provided a vehicle control system comprising: a map informationoutputting means for outputting map information including a road onwhich a subject vehicle travels; a subject-vehicle position detectingmeans for detecting a subject-vehicle position on a map; a steeringmeans for steering a steering control wheel of the vehicle, asteering-torque applying means for applying a steering torque to thesteering means; and a control means for determining a required steeringtorque based on an azimuth change quantity of the road on which thevehicle is traveling, and for driving the steering-torque applying meansbased on the steering torque.

With the above arrangement, the required steering torque is determinedbased on the azimuth change quantity of the road on which the vehicle istraveling, and a steering torque is applied to the steering means basedon such required steering torque. Therefore, even if the driver has alowered driving capability, the possibility of the departing of thevehicle from the road can be reduced remarkably.

To achieve the first object, according to the present invention, thereis provided a vehicle control system comprising: a map informationoutputting means for outputting map information including a road onwhich a subject vehicle travels; a subject-vehicle position detectingmeans for detecting a subject-vehicle position on a map; a warningindicating means for giving a warning to a driver; and a control meansfor determining a deviation between an azimuth change quantity of theroad on which the vehicle is traveling and an azimuth change quantity ofthe vehicle, and for driving the warning indicating means based on thedeviation.

With the above arrangement, the deviation between the azimuth changequantity of the road on which the vehicle is traveling and the azimuthchange quantity of the vehicle, and the warning is given to the driverbased on the deviation. Therefore, even if the driver has a lowereddriving capability, the possibility of the departing of the vehicle fromthe road can be reduced remarkably.

To achieve the first object, according to the present invention, thereis provided a vehicle control system comprising: a map informationoutputting means for outputting map information including a road onwhich a subject vehicle travels; a subject-vehicle position detectingmeans for detecting a subject-vehicle position on a map; a steeringmeans for steering a steering control wheel of the vehicle; asteering-torque applying means for applying a steering torque to thesteering means; a reference yaw rate determining means for estimating ayaw rate generated during traveling of the vehicle based on the shape ofa road ahead of the subject-vehicle position on the travel road todetermine the estimated yaw rate as a reference yaw rate; an actual yawrate detecting means for detecting an actual yaw rate; and a controlmeans for determining a deviation between the reference yaw rate and theactual yaw rate to drive the steering-torque applying means such as todecrease the deviation.

With the above arrangement, the deviation between the reference yaw ratebased on the an azimuth change quantity of the road on which the vehicleis traveling and the actual yaw rate of the vehicle, is determined, andthe steering torque is applied to the steering means in the direction todecrease the deviation. Therefore, even if the driver has a lowereddriving capability, the possibility of the departing of the vehicle fromthe road can be reduced remarkably.

To achieve the second object, according to the present invention, thereis provided a vehicle control system comprising: a map informationoutputting means for outputting map information including a road onwhich a subject vehicle travels; a subject-vehicle position detectingmeans for detecting a subject-vehicle position on a map; a travelingstate detecting means for detecting a traveling state of the vehicle; asteering means for steering a steering control wheel of the vehicle; asteering-torque applying means for applying a steering torque to thesteering means; a steerage control means for determining asteering-toque application quantity based on the traveling state of thevehicle and the shape of a road ahead of the subject-vehicle position onthe travel road to drive the steering-torque applying means based on thesteering-torque application quantity; an ahead-traveling vehicledetecting means for detecting a distance between the subject vehicle andan ahead-traveling vehicle and/or a relative speed of the subjectvehicle relative to the ahead-traveling vehicle; a follow-up travelcontrol means for controlling the distance between the subject vehicleand the ahead-traveling vehicle to allow the subject vehicle to travelwhile following the ahead-traveling vehicle in accordance with thedistance between the subject vehicle and the ahead-traveling vehicleand/or the relative speed of the subject vehicle relative to theahead-traveling vehicle; and a control switch-over means whichdiscontinues a steerage control by the steerage control means when afollow-up control by the follow-up control means is started during thesteerage control, and which starts the steerage control by the steeragecontrol means when the vehicle control system fails to detect theahead-traveling vehicle during the follow-up travel control by thefollow-up travel control means.

With the above arrangement, when the follow-up travel control by thefollow-up travel control means is started during the steerage control bythe steerage control means, the steerage control is discontinued, andwhen the ahead-traveling vehicle is failed to be detected during thefollow-up travel control by the follow-up travel control means, thesteerage control is started. Therefore, it is possible to exhibit thefunctions of both the follow-up travel control and the steerage controlwithout causing the driver to feel a sense of incompatibility and atroublesomeness due to a mutual interference of the follow-up travelcontrol and the steerage control.

To achieve the second object, according to the present invention, thereis provided a vehicle control system comprising: a map informationoutputting means for outputting map information including a road onwhich a subject vehicle travels; a subject-vehicle position detectingmeans for detecting a subject-vehicle position on a map; a vehicle speeddetecting means for detecting a vehicle speed; a passability orimpassability determining means for determining whether the vehicle canpass through a road ahead of the subject-vehicle position, based on thevehicle speed and the shape of the road ahead of the subject-vehicleposition; a vehicle speed control means for controlling the vehiclespeed based on the determination by the passability or impassabilitydetermining means; an ahead-traveling vehicle detecting means fordetecting a distance between the subject vehicle and an ahead-travelingvehicle and/or a relative speed of the subject vehicle relative to theahead-traveling vehicle; a follow-up travel control means forcontrolling the distance between the subject vehicle and theahead-traveling vehicle to allow the subject vehicle to travel whilefollowing the ahead-traveling vehicle in accordance with the distancebetween the subject vehicle and the ahead-traveling vehicle and/or therelative speed of the subject vehicle relative to the ahead-travelingvehicle; and a control switch-over means which discontinues a vehiclespeed control by the vehicle speed control means when a follow-upcontrol by the follow-up control means is started during the vehiclespeed control by the vehicle speed control means, and which starts thevehicle speed control by the vehicle speed control means when thevehicle control system fails to detect the ahead-traveling vehicleduring the follow-up travel control by the follow-up travel controlmeans.

With the above arrangement, when the follow-up control by the follow-upcontrol means is started during the vehicle speed control by the vehiclespeed control means, the vehicle speed control is discontinued and whenthe ahead-traveling vehicle is failed to be detected during thefollow-up travel control by the follow-up travel control means, thevehicle speed control by the vehicle speed control means is started.Therefore, it is possible to exhibit the functions of both the vehiclespeed control and the follow-up travel control without causing thedriver to feel a sense of incompatibility and a troublesomeness due to amutual interference of the vehicle speed control and the follow-uptravel control.

To achieve the third object, according to the present invention, thereis provided a vehicle control system comprising: a map informationoutputting means for outputting map information including a road onwhich a subject vehicle travels; a subject-vehicle position detectingmeans for detecting a subject-vehicle position on a map; a steeringmeans for steering a steering control wheel of the vehicle; asteering-torque applying means for applying a steering torque to thesteering means; a steering angular velocity detecting means fordetecting a steering angular velocity input to the steering means; and asteerage control means which determines a steering-torque applicationquantity based on a traveling state of the vehicle and the shape of aroad ahead of the subject-vehicle position on the travel road to drivethe steering-torque applying means, and which corrects thesteering-torque application quantity, when a steering angular velocityequal to or larger than a predetermined value is detected by thesteering angular velocity detecting means.

With the above arrangement, when the driver has found an obstacle aheadand has conducted an obstacle avoiding operation while preventing thedeparting of the vehicle from the road by applying the steering torqueto the steering means based on the traveling state of the vehicle andthe shape of the road district ahead of the subject-vehicle position,the steering torque can be corrected to reliably conduct the avoidingoperation. At this time, it can be detected based on the magnitude ofthe steering angular velocity that the driver has conducted the avoidingoperation.

To achieve the third object, according to the present invention, thereis provided a vehicle control system comprising: a map informationoutputting means for outputting map information including a road onwhich a subject vehicle travels; a subject-vehicle position detectingmeans for detecting a subject-vehicle position on a map; a steeringmeans for steering a steering control wheel of the vehicle; asteering-torque applying means for applying a steering torque to thesteering means; an ahead-obstacle detecting means for detecting anobstacle ahead of the vehicle; a side-obstacle detecting means fordetecting an obstacle sideways of the vehicle; and a steerage controlmeans which determines a steering-torque application quantity based on atraveling state of the vehicle and the shape of a road ahead of thesubject-vehicle position on the travel road to drive the steering-torqueapplying means, and which corrects the steering-torque applicationquantity such as to avoid an obstacle ahead of the subject vehicle ifsuch an obstacle is detected by the ahead-obstacle detecting means, andcorrects the steering-torque application quantity in a direction reversefrom the direction to avoid the obstacle, if the side-obstacle detectingmeans detects that the subject vehicle has avoided the obstacle.

With the above arrangement, the avoidance of the obstacle and thereturning of the vehicle to a travel lane can be reliably performed bycorrecting the steering torque in the direction to avoid the obstacle,if the obstacle has been detected ahead by the ahead-obstacle detectingmeans, and by correcting the steering torque in the direction reversefrom the direction to avoid the obstacle if it is detected by theside-obstacle detecting means that the subject vehicle has avoided theobstacle, while preventing the departing of the subject vehicle from theroad by applying the steering torque to the steering means based on thetraveling state of the vehicle and the shape of the road districtexisting ahead of the subject-vehicle position on the travel road.

The above and other objects, features and advantages of the inventionwill become apparent from the following detailed description ofpreferred embodiments taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the entire arrangement of a vehiclecontrol system according to a first embodiment of the present invention;

FIG. 2 is a flowchart for explaining the operation;

FIG. 3 is a diagram for explaining a method for determining an azimuthchange quantity of a road;

FIG. 4 is a flowchart according to a second embodiment of the presentinvention;

FIG. 5 is a flowchart according to a third embodiment of the presentinvention;

FIG. 6 is a flowchart according to a fourth embodiment of the presentinvention;

FIG. 7 is a diagram for explaining a fifth embodiment;

FIG. 8 is a block diagram showing the entire arrangement of a vehiclecontrol system according to a sixth embodiment of the present invention;

FIG. 9 is a flowchart of a steerage control routine;

FIG. 10 is a graph illustrating the relationship between the deviationand the steerage assisting torque T;

FIG. 11 is a graph illustrating the relationship between the steeringangle θ_(ST) and the steerage assisting torque T;

FIG. 12 is a flowchart of a steerage control discontinuing routine;

FIG. 13 is a diagram for explaining another method for determining anazimuth change quantity of a road according to a seventh embodiment ofthe present invention;

FIG. 14 is a diagram for explaining a further method for determining anazimuth change quantity of a road according to a eighth embodiment ofthe present invention;

FIG. 15 is a block diagram showing the entire arrangement of a vehiclecontrol system according to a ninth embodiment of the present invention;

FIG. 16 is a flowchart of a follow-up travel control routine;

FIG. 17 is a diagram for explaining the operation during a follow-uptravel control;

FIG. 18 is a block diagram showing the entire arrangement of a vehiclecontrol system according to a tenth embodiment of the present invention;

FIG. 19 a flowchart of a vehicle speed control routine;

FIG. 20 is a diagram for explaining the operation during traveling of avehicle at a low vehicle speed;

FIG. 21 is a diagram for explaining the operation during traveling ofthe vehicle at a high vehicle speed;

FIG. 22 is a diagram for explaining the operation when a road lieswithin a passable area;

FIG. 23 is a diagram for explaining the operation when a road liesoutside the a passable area;

FIG. 24 is a diagram for explaining a method for determining a passablevehicle speed;

FIG. 25 is a block diagram showing the entire arrangement of a vehiclecontrol system according to an eleventh embodiment of the presentinvention;

FIG. 26 is a flowchart for explaining the operation;

FIG. 27 is a diagram for explaining the operation when an obstacle isavoided;

FIG. 28 block diagram showing the entire arrangement of a vehiclecontrol system according to a twelfth embodiment of the presentinvention; and

FIG. 29 is a diagram for explaining the operation when an obstacle isavoided.

Each of step numbers used in each of the embodiments is concluded in theembodiment, and even if the same step numbers are used in differentembodiments, the contents thereof are not necessarily the same.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, a first embodiment of the present invention will now be describedwith reference to FIGS. 1 to 3. Referring to FIG. 1, reference characterNV is a navigation system for a vehicle. The navigation system NVincludes an inertial navigating device 3 into which signals from a yawrate sensor 1 and a vehicle speed sensor 2 are input, a map informationoutputting means 4 using an IC card or CD-ROM, and a map matching means5 for superposing a travel locus along which a subject vehicle travelsand which is output by the inertial navigating device 3, onto a mapinformation output by the map information outputting means 4. Thenavigation system NV further includes a GPS unit 7 into which a signalfrom a GPS antenna 6 is input, a subject-vehicle position detectingmeans 8 for detecting the position of the subject vehicle based onposition coordinates output by the map matching means 5 and positioncoordinates output by the GPS unit 7, and a course searching means 10for searching a course to a destination based on destination coordinatesfrom a destination inputting means 9 and subject-vehicle positioncoordinates from the subject-vehicle position detecting means 8.

Reference character SC is a steerage control section. The steeragecontrol section SC includes an azimuth detecting means 11 for detectingan azimuth change quantity θ of a road ahead of the subject vehicle,based on a signal from the course searching means 10, a control means 13which determines whether there is a possibility of the departing of thevehicle from a road, based on signals from the yaw rate sensor 1, thevehicle speed sensor 2, a steering angle sensor S₁ and the azimuthdetecting means 11, a steering torque applying means 14 for applying apredetermined steering torque to a steering means 15 for steering asteering control wheel, based a signal from the control means 13, awarning indicating means 17 such as a buzzer, a chime, a lamp, a displayand the like for giving a warning to a driver, based on the signal fromthe control means 13, and a regulating means 16 for regulating themotion of the steering torque applying means 14, based on the signalfrom the course searching means 10. The steering torque applying means14 is, for example, an actuator for an electric power-steering device,or the like.

Among the above-described various means, the steering angle sensor S₁,the regulating means 16 and the warning indicating means 17, which aresurrounded by a dashed line, are not used in the first embodiment and asecond embodiment. The steering angle sensor S₁ and the warningindicating means 17 are used in a third embodiment, and the regulatingmeans 16 is used in a fifth embodiment.

The operation of the first embodiment of the present invention will bedescribed below with reference to a flowchart in FIG. 2.

First, it is determined based on an output from the course searchingmeans 10 whether there is a curve in a road within a predetermined rangeahead of the subject vehicle (step S1). If the answer at step S1 is YESto indicate that there is a curve, a yaw rate γ is read from the yawrate sensor 1 to conduct a steerage control suitable for the passage ofthe vehicle through such curve; a vehicle speed V₀ is read from thevehicle sensor 2, and road data are read from the course searching means8 (step S2).

As can be seen from FIG. 3, the road ahead of the subject vehicle, whichhas been searched by the course searching means 10, is comprised of aset of a large number of nodes N, and first, second, third and fourthreference nodes N₁, N₂, N₃ and N₄ are selected from the set of thenodes. At this time, the second reference node N₂ is set at the positionof the subject vehicle detected by the subject-vehicle positiondetecting means 8; the first reference node N₁ is set at a positionshort of the second reference node N₂ by a distance a; the thirdreference node N₃ is set at a position ahead of the second referencenode N₂ by a distance a; and the fourth reference node N₄ is set at aposition ahead of the third reference node N₃ by a distance a. Here, ais determined as a product of the vehicle speed V₀ and a predeterminedtime t₁ (a=V₀ ×t₁).

By determining the distance a between the reference nodes N₁, N₂, N₃, N₄in the above manner, the distance between the reference nodes N₁, N₂, N₃and N₄ , when the vehicle speed V₀ is large, can be determined at alarge value to insure calculating time enough to calculate the azimuthchange quantity θ of the road which will be described hereinafter.

When no node N exists at a temporary position of the subject vehicle orat a position established by a multiple of the distance a on the basisof a temporary position of the subject vehicle, the node N nearest tosuch position is extracted as the reference node N₁, N₂, N₃, N₄. Whenthe data for the node N is sparse and no node N exists in a range of thedistance a, four consecutive nodes N are extracted as the referencenodes N₁, N₂, N₃ and N₄.

Provided that the road is of a curved shape and four reference nodes N₁,N₂, N₃ and N₄ exist substantially on an arc, a quantity θ of azimuthchange from the second reference node N₂ which is the position of thesubject vehicle to the next third reference node N₃ is determined in theazimuth change quantity detecting means 11 in the following manner:

First, the following vectors are calculated: a vector V₁₂ (X₁₂, Y₁₂)connecting the first reference node N₁ (X₁, Y₁) and the second referencenode N₂ (X₂, Y₂); a vector V₂₃ (X₂₃, Y₂₃) connecting the secondreference node N₂ (X₂, Y₂) and the third reference node N₃ (X₃, Y₃); anda vector V₃₄ (X₃₄, Y₃₄) connecting the third reference node N₃ (X₃, Y₃)and the fourth reference node N₄ (X₄, Y₄).

At this time, if an angle formed by the vectors V₁₂ and V₂₃ isrepresented by θ₁, an equation,

    X.sub.12 ×x.sub.23 +Y.sub.12 ×Y.sub.23 =(X.sub.12.sup.2 +Y.sub.12.sup.2).sup.1/2 ×(x.sub.23.sup.2 +Y.sub.23.sup.2).sup.1/2 ×cos θ.sub.1                                  (1)

is established from an inner product of the vectors V₁₂ and V₂₃, and theangle θ₁ is calculated from this equation.

In addition, if an angle formed by the vectors V₂₃ and V₃₄ isrepresented by θ₂, an equation,

    X.sub.23 ×x.sub.34 +Y.sub.23 ×Y.sub.34 =(X.sub.23.sup.2 +Y.sub.23.sup.2).sup.1/2 ×(X.sub.23.sup.2 +Y.sub.34.sup.2).sup.1/2 ×cos θ.sub.2                                  (2)

is established from an inner product of the vectors V₂₃ and V₃₄, and theangle θ₂ is calculated from this equation.

Thus, a quantity θ of azimuth change from the second reference node N₂to the third reference node N₃ is given from an equation,

    θ=(θ.sub.1 +θ.sub.2)/2                   (3)

When the azimuth change quantity θ of the road (i.e., the quantity θ ofazimuth change between the second and third nodes N₂ and N₃) iscalculated in the above manner, steps S4 to S10 which will be describedbelow are then carried out in the control means 13.

When a time δt has been lapsed and the vehicle has reached the thirdnode N₃ from the second node N₂ (at step S4), an azimuth change quantityΘ of the vehicle is calculated by integrating the yaw rate γ from t=0 tot=δt in the control means 13 (at step S5). The azimuth change quantity Θof the vehicle corresponds to a quantity of change in yaw angle whilethe vehicle reaches the third node N₃ from the second node N₂. Then, adeviation D (=|θ-Θ|) between the azimuth change quantity θ of the roaddetermined at step S3 and the azimuth change quantity Θ of the vehicledetermined at step S5 is calculated (at step S6). The deviation D iscompared with a reference value β which is determined in accordance withthe width W of the road (at step S7). The reference value β can bedetermined according to the following expression, as a value whichensures that the vehicle does not depart from the road having a width W,for example, while the vehicle is traveling over the distance a from thesecond reference node N₂ to the third reference node N₃.

    A×β<W/2                                         (4)

If the answer at step S7 is YES indicate that the deviation D is smallerthan the reference value β, it is determined that there is nopossibility that the vehicle will depart from the road, and the steeragecontrol is not conducted(at step S8). On the other hand, if the answerat step S7 is NO to indicate that the deviation D is equal to or largerthan the reference value β, it is determined that there is a possibilitythat the vehicle will depart from the road, and a steering torque forconverging the deviation D to zero is calculated (at steps S9 and S10).The steering torque applying means 14 is allowed to act on the steeringmeans 15 by the steering torque, thereby facilitating the returning ofthe vehicle to the travel line by a driver (at steps S11 and S12) Theexecution of such a feedback control ensures that even if the driver isunskilled in driving technique, or if a driver's driving capability islowered due to a fatigue or the like, it is facilitated for the azimuthchange quantity Θ of the vehicle to automatically follow the azimuthchange quantity θ of the road, whereby the possibility of the departingof the vehicle from the road can be remarkably reduced.

A second embodiment of the present invention will now be described withreference to a flowchart in FIG. 4. In the first embodiment, thesteering means 15 is feedback-controlled, whereas the steering means 15is feedforward-controlled in the second embodiment.

Steps S1 to S3 in the flowchart shown in FIG. 4 are substantially thesame as steps S1 to S3 in the flowchart shown in FIG. 2. At steps S1 toS3, an azimuth change quantity θ of a road is calculated. However, atstep S2 in the flowchart shown in FIG. 4, the reading of a yaw rate isnot carried out.

Then, a target steering torque to be output by the steering torqueapplying means 14 is calculated based on a time-differentiation value ofthe azimuth change quantity θ in the control means 13 (at step S13), andthe steering device 15 is driven based on the target steering torque (atstep S14). When the vehicle has reached the third reference node N₃ fromthe second reference node N₂, the above-described operation is repeatedbased on new reference nodes N₁, N₂, N₃ and N₄ (at step S15).

In the second embodiment, the steering device 15 isfeedforward-controlled so that the vehicle follows a previously detectedazimuth change quantity θ of the road and hence, the vehicle can bereliably guided along the road to help the driver's driving operation.

A third embodiment of the present invention will now be described withreference to a flowchart in FIG. 5. In the third embodiment, both of thefeedback control and the feedforward control are used in combination.

First, a yaw rate γ is read from the yaw rate sensor 1; a vehicle speedV₀ of the subject vehicle is read from the vehicle speed sensor 2; asteering angle θ_(STRG) is read from the steering angle sensor S₁ andfurther, a position P₀ of the subject vehicle is read (at step A21).

Then, an azimuth change quantity Θ' of the vehicle from t=0 to t=δt iscalculated based on the steering angle θ_(STRG) (at step S22). Morespecifically, a turning radius R for the vehicle traveling at thesteering angle θ_(STRG) and the vehicle speed V₀ is given according tothe following equation:

    R=(1+AV.sub.0.sup.2)×L×N/θ.sub.STRG      (5)

wherein A is a stability factor; L is a wheel base; and N is a steeringgear ratio. Therefore, the azimuth change quantity Θ' of the vehiclefrom t=0 to t=δt based on the steering angle θ_(STRG) is given accordingto the following equation:

    Θ'=V.sub.0 ×δt/R=θ.sub.STRG ×V.sub.0 ×δt/{(1+AV.sub.0.sup.2)×L×N}      (6)

Then, an azimuth change quantity Θ of the vehicle from t=δt to t=0 iscalculated by integrating the yaw rate γ from t=-δt to t=0 (at stepS23).

Subsequently, four nodes N₁, N₂, N₃ and N₄ extracted from the road dataare extracted (at step S24), and an azimuth change quantity θf of theroad from t=0 to t=δt is calculated based on the nodes N₁, N₂, N₃ and N₄(at step S25) This azimuth change quantity θf of the road is calculatedin the same manner as is the azimuth change quantity θ of the roadcalculated at step S3 in the flowchart (see FIG. 2) in the firstembodiment.

Then, other four nodes N₁, N₂, N₃ and N₄ at positions short of theabove-described four node N₁, N₂, N₃ and N₄ by an increment of adistance a are extracted (at step S26), and an azimuth change quantityθb of the road from t=-δt to t=0 is calculated based on these nodes N₁,N₂, N₃ and N₄ (at step S27) . The azimuth change quantity θb of the roadis also calculated in the same manner as is the azimuth change quantityθ of the road calculated at step S3 in the flowchart (see FIG. 2) in thefirst embodiment.

A deviation between the azimuth change quantity θb of the road fromt=-δt to t=0 determined at step S27 and the azimuth change quantity Θ ofthe vehicle from t=-δt to t=0 determined at step S23 is compared with apredetermined reference value k (at step S28). If the answer at step S28is YES to indicate that the deviation exceeds the reference value k, thesteering torque applying means 14 feedback-controls the steering device15 with a predetermined steering torque in order to converge thedeviation into zero to avoid the departing of the vehicle from the road(at step S29).

If the answer at step S28 is NO to indicate that the deviation is equalto or smaller than the reference value k, a deviation between theazimuth change quantity Θ' of the vehicle from t=0 to t=δt calculated atstep S22 and the azimuth change quantity θf of the road from t=0 to t=δtcalculated at step S25 is compared with a predetermined reference valuem (at step S30). If the answer at step S30 is YES to indicate that thedeviation exceeds the reference value m, the steering torque applyingmeans 14 feedforward-controls the steering device 15 with apredetermined steering torque in order to previously prevent thegeneration of the deviation to avoid the departing of the vehicle fromthe road, and a warning is given to the driver by the warning indicatingmeans 17 (at step S31).

By using the feedback control excellent in convergence and thefeedforward control excellent in responsiveness in combination, asdescribed above, the possibility of the departing of the vehicle fromthe road can be further reduced.

When the driver is unskilled in driving technique, or has a lowereddriving capability, it is effective that the steering device 15 iscontrolled to avoid the departing of the vehicle from the road. However,when the driver has a normal driving level, the steering conducted bythe driver himself while perceiving a curve may interfere with thesteerage control in some cases. In such a case, the driver's intentionis preferential, and the steerage control is discontinued. The detailsthereof will be described as a fourth embodiment with reference to aflowchart in FIG. 6.

First, if it is determined that there is a possibility that the vehiclewill depart from the road (at step S41), the steerage control describedin the first, second and third embodiments, when the vehicle speed V₀exceed 30 km/hr (at step S42), is carried out to avoid the departing ofthe vehicle from the road (at step S43). When the vehicle speed V₀ isequal to or lower than 30 km/hr, i.e., during steerage at a largesteering angle, the steerage control is not carried out.

When the steerage control has been carried out at step S43, the amountof change in accelerator opening degree exceeds a predetermined value(at step S44), the steerage control is stopped (at step S49).

Likewise, when the steerage control has been carried out at step S43,the steerage control is stopped, if the braking operation has beenconducted (at step S45), if the rate of change in steering angleθ_(STRG) with time, i.e., the angular exceeds a predetermined value (atstep S46), the steerage control is stopped at step S49, if the steeringtorque provided by the driver's spontaneous steerage exceeds apredetermined value (at step S47) and if the winker operation has beenconducted (at step S48).

In this way, when the driver is in a normal condition and is conductingany driving operation with his own intention, the steering operationconducted by the driver himself is in preference to the steeragecontrol, thereby avoiding the interference of the driver's steeringoperation and the steerage control with each other.

The conceivable purposes of the steerage control described in the firstto fourth embodiments are not only to merely avoid the departing of thevehicle from the road, but also to enhance the steerage feeling and thetravel stability by conducting the steerage suitable for a road districtsuch as a highway, a winding road, an urban area and the like.

A fifth embodiment achieves such purposes. In the fifth embodiment, thevalue of a steering torque applied to the steering means 15 by thesteering torque applying means 14 is regulated by the regulating means16 (see FIG. 1) to which a road district is input from the coursesearching means 10.

For example, if the road district is a highway, the straight advancingproperty against an external disturbance such as a side wind, a wheeltrack and the like can be enhanced by setting the gain of the steeringtorque determined by the steering torque applying means 14 in a higherrange in the vicinity of the neutral, as shown in FIG. 7A. If the roaddistrict is a winding road, the interference with the driver'sspontaneous steering operation can be avoided to enhance themaneuverability by setting the gain of the steering torque determined bythe steering torque applying means 14 in a lower range in the vicinityof the neutral, as shown in FIG. 7B. Further, if the road district is anurban area, the moderate compatibility of the straight advancingproperty and the maneuverability can be provided by setting the gain ofthe steering torque at a given value, as shown in FIG. 7C.

Even in the above-described first and second embodiments, if there is apossibility that the vehicle will depart from the road, the warningindicating means 17 can be operated.

A sixth embodiment of the present invention will now be described withreference to FIGS. 8 to 12. As can be seen from FIG. 8, a steeragecontrol section SC in the sixth embodiment includes a reference yaw ratedetermining means 18 for determining a yaw rate presumed to be generatedwhen the subject vehicle will travel on a road ahead of the subjectvehicle, as a reference yaw rate γ_(REF) based on the shape of the roadsearched by the course searching means 10, a control means 13 whichcompares an actual yaw rate γ detected by the yaw rate sensor 1 with thereference yaw rate γ_(REF) and calculates a steerage assisting torque Tin accordance with a deviation between the yaw rates γ_(REF) and γ, asteering torque applying means 14 for applying the steerage assistingtorque T to a steering means 15 for steering the steering control wheelbased on a signal from the control means 13, and a regulating means 16for regulating the motion of the steering torque applying means 14 basedon a signal from the course searching means 10. Here, the steeringtorque applying means 14 is, for example, an actuator for an electricpower-steering device, or the like.

A steering angle sensor S₂, a steering torque sensor S₃, an acceleratoropening degree S₄, a braking pressure sensor S₅ and a directionindicator S₆ are connected to the control means 13 in order todiscontinue the steerage control when a predetermined condition has beenrealized.

The operation of the sixth embodiment of the present invention will bedescribed below with reference to a flowchart in FIG. 9.

First, the position of the subject vehicle on a map and data for a roadahead of the subject vehicle position are read by the navigation systemNV (steps S1 and S2).

An azimuth change quantity θ of the road (i.e., an azimuth changequantity θ between a second node N₂ and a third node N₃ is calculatedbased on FIG. 3 and according to the above-described equation (3) (atstep SS3). A reference yaw rate γ_(REF) is calculated by dividing suchazimuth change quantity θ by a time δt required for the vehicle totravel from the second reference node N₂ to the third reference node N₃(at step S4).

    γ.sub.REF =θ/δt                          (7)

Then, an actual yaw rate γ is read from the yaw rate sensor 1 (at stepS5), and a deviation D between the reference yaw rate γ_(REF) calculatedat step S4 and the actual yaw rate γ determined at step S5 is calculated(at step S6). A steerage assisting torque T (T=kD) proportional to thedeviation D is determined (at step S7). For example, when the deviationD is positive as shown in FIG. 10, a steerage assisting torque Tpermitting the steering control wheel to be steered rightwardly isprovided to the steering means 15. When the deviation D is negative, asteerage assisting torque T permitting the steering control wheel to besteered leftwardly is provided to the steering means 15.

A dashed line in FIG. 11 indicates a steering characteristic in a normalcondition. A steerage assisting torque T according to a steering angleθ_(ST) of a steering control wheel is generated, but when there is apossibility that the vehicle will depart leftwardly from a course, thesteering characteristic is controlled from a condition shown by dashedline to a condition shown in a solid line. As a result, a predeterminedsteerage assiting torque T permitting the steering control wheel to besteered rightwardly is generated, even if the steering control wheel isnot steered (i.e., even if the steering angle θ_(ST) =0) Thus, thevehicle is assisted to return to a correct course.

By conducting such feedback control, even if the driver is unskilled indriving technique or has a lowered driving capability due to fatigue, itis facilitated for the locus of traveling of the vehicle to follow theshape of the road, whereby the possibility of the departing of thevehicle from the road can be remarkably reduced.

When the driver is unskilled in driving technique or has a lowereddriving capability due to fatigue, it is effective that the steeringmeans 15 is controlled to avoid the departing of the vehicle from theroad, as described above. However, when the driver is at a normal level,the steering operation conducted by the driver himself while perceivinga curve may interfere with the steerage control in some cases. In such acase, the driver's intention is preferential, and the steerage controlis discontinued. The details thereof will be described below withreference to a flowchart in FIG. 12.

First, when a deviation is generated between the reference yaw rateγ_(REF) and the actual yaw rate γ and it is determined that there is apossibility that the vehicle will depart from the road (at step S11),the steerage control, when the vehicle speed V exceeds 30 km/hr (at stepS12), is carried out to avoid the departing of the vehicle from the road(at step S13). When the vehicle speed V is equal to or lower than 30km/hr (at step S12), i.e., during traveling of the vehicle at a lowerspeed attendant with a possibility that the steering operation at alarger steering angle b is conducted, the steerage control is notcarried out.

Now, when the steerage control has been conducted at step S13, thesteerage control is stopped (at step S19), if the amount of variation inaccelerator opening degree detected by the accelerator opening degreesensor S₄ exceeds a predetermined value (at step S14).

Likewise, when the steerage control has been carried out at step S13,the steerage control is stopped, if the amount of change in brakingpressure detected by the braking pressure sensor S₅ exceeds apredetermined value (at step S15), if the rate of change in steeringangle θ_(ST) detected by the steering angle sensor S₂ with time, i.e.,the steering angular velocity exceeds a predetermined value (at stepS16), if the steering torque provided by the driver's spontaneoussteering operation and detected by the steering torque sensor S₃ (atstep S17), if the operation of the direction indicator S₆ is conducted(st step S18), and if the steering torque detected by the steeringtorque sensor S₃ is approximately zero and the driver does not grasp thesteering wheel (at step S19).

In this way, when the driver is in a normal condition and is conductingany driving operation with his own intention, the steering operationconducted by the driver himself is preferential to the steerage control,thereby avoiding the interference of the driver's steering operation andthe steerage control with each other. If a steerage assisting torque Tis applied when the driver has released his hand from the steering wheeldue to dozing, a problem of cutting of the steering in such a directionis encountered. However, the application of an unnecessary steerageassisting torque is avoided by discontinuing the steerage control bystep S19.

The conceivable purposes of conducting the steerage are not only tomerely avoid the departing of the vehicle from the road, but also toenhance the steerage feeling and the travel stability by conducting thesteerage suitable for a road district such as a highway, a winding road,an urban area and the like.

To achieve such purpose, the value of a steering torque applied to thesteering means 15 by the steering torque applying means 14 is regulated,as described with reference to FIG. 7, by the regulating means 16 (seeFIG. 8) to which a road district is input from the course searchingmeans 10.

A seventh embodiment of the present invention will now be described.

In the previous sixth embodiment, the azimuth change quantity θ betweenthe second reference node N₂ which is the position of the subjectvehicle and the third reference node N₃ ahead of the position of thesubject vehicle is calculated. However, when a map data with a verylarge number of data quantity and a high node density is used, theazimuth change quantity θ to three pr more nodes (i.e., from the secondnode N₂ to a n-th node N_(n)) can be calculated by a technique shown inFIG. 13.

If the nodes existing within a distance S determined by multiplying apredetermined time δt and a vehicle speed by each other are representedby N₂, N₃,--N_(n). In this case, the node N₁ is a node short of theposition of the subject vehicle, and the node N₂ is a node which is atthe position of the subject vehicle. As can be seen from FIG. 13, theazimuth change quantity θ from the node N₂ to the node N_(n) is providedaccording to the following equation:

    θ=(θ.sub.1 /2)+θ.sub.2 +θ.sub.3 +--θ.sub.n-2 +(θ.sub.n-1 /2)                                     (8)

θ₁ to θ_(n-1) can be calculated in the same manner as the equations (1)and (2), and the equation (3) corresponds to the equation (8) in which nis 3.

The reference yaw rate γ_(REF) is calculated by dividing the azimuthchange quantity θ calculated according to the equation (8) by the timeδt.

When a map data with a low node density is used, the azimuth changequantity θ can be calculated using three nodes N₁, N₂ and N₃.

When the position of the subject vehicle lies at the middle pointbetween the nodes N₁ and N₂, the azimuth change quantity θ from theposition of the subject vehicle to the middle point between the nodes N₁and N₂ is equal to an angle θ formed by vectors V₁₂ and V₂₃, the θ beingprovided according to the equation (7). If the distance between thenodes N₁ and N₂ is represented by L₁ and the distance between the nodesN₂ and N₃ is represented by L₂, the time δt required for the vehicle totravel over a distance (L₁ +L₂)/2 from the middle point between thenodes N₁ and N₂ to the middle point between the nodes N₂ and N₃ is equalto (L₁ +L₂)/2V. Therefore, the reference yaw rate γ_(REF) is providedaccording to the following equation:

    γ.sub.REF =2θV/(L.sub.1 +L.sub.2)              (9)

A ninth embodiment of the present invention will now described withreference to FIGS. 15 to 17. In FIG. 15, the arrangement of a navigationsystem NV and the structure of a steerage control section SC aresubstantially the same as those in the sixth embodiment shown in FIG. 8.The steerage control section SC in the ninth embodiment does notincludes the regulating means 16 described with reference to FIG. 8, butof course, the regulating means 16 can be added.

Reference character FC is a follow-up travel control section whichincludes a radar sensor S₆, an ahead-traveling vehicle detecting meansS₇ for detecting whether there is a vehicle traveling ahead of thesubject vehicle (which will be referred to as an ahead-traveling vehiclehereinafter), a distance between the subject vehicle and theahead-traveling vehicle, a relative speed between the subject vehicleand the ahead-traveling vehicle and the like, based on a signal from theradar sensor S₆, and a follow-up travel control means 20 for allowingthe subject vehicle to travel while following the ahead-travelingvehicle, based on signals from the ahead-traveling vehicle detectingmeans S₇, the vehicle speed sensor 2 and the follow-up starting switch19. A vehicle speed regulating means 21 regulates the vehicle speed,based on a signal from the follow-up travel control means 20, therebymaintaining the distance between the subject vehicle and theahead-traveling vehicle constant. The vehicle speed regulating means 21is, for example, a well-known automatic cruising device.

The signals from the ahead-traveling vehicle detecting means S₇ and thefollow-up starting switch 19 are input into a control switching means 22which is connected the control means of the steerage control section SCand the follow-up travel control means 20 of the follow-up travelcontrol section FC.

The function of the follow-up travel control section FC will bedescribed below with reference to a flowchart in FIG. 16.

First, when the follow-up starting switch 19 of the follow-up travelcontrol section FC is depressed (at step S11), the ahead-travelingvehicle detecting means S7 determines a distance and a relative speed ofthe subject vehicle relative to the ahead-traveling vehicle and, basedon the signal from the radar sensor S₂, and the follow-up travel controlmeans 20 controls the vehicle speed regulating means 21 to maintain apredetermined vehicle-vehicle distance suitable for the relative speed,thereby starting the control of the follow-up travel with respect to theahead-traveling vehicle (at step S12). At this time, if the steeragecontrol by the steerage control section SC is being carried out (at stepS13), the steerage control by the steerage control section SC isdiscontinued in order to avoid the interference of both the follow-uptravel control and the steerage control with each other (at step S14).

When the ahead-traveling vehicle has suddenly changed course to leave arange available for the radar sensor S₆ and the ahead-traveling vehicledetecting means S₇ has lost sight of the ahead-traveling vehicle (atstep S15), the follow-up travel control by the follow-up travel controlsection FC is discontinued (at step S16). At this time, when the currentcondition is such that the steerage control has been in progress at stepS13 and the steerage control has been discontinued at step S14 (at stepS17), the steerage control is restarted (at step S18). Thus, if thefollow-up travel control becomes impossible, the follow-up travelcontrol can be restored quickly to the steerage control withoutconducting a special operation.

On the other hand, when the steerage control has not been discontinuedat step S17, i.e., when the steerage control has not been originallycarried out, if the ahead-traveling vehicle once lost sight of or a newahead-traveling vehicle is found (at step S19), the control of thefollow-up travel with respect to the found ahead-traveling vehicle isrestarted.

A tenth embodiment of the present invention will now be described withreference to FIGS. 18 to 24.

As shown in FIG. 18, the arrangement of a navigation system NV and thestructure of a follow-up travel control section FC are the same as inthe ninth embodiment, but the tenth embodiment is different from theninth embodiment in that a cornering control section CC is included inplace of the steerage control section SC used in the ninth embodiment.

The cornering control section CC includes a passability/impassabilitydetermining means 23 for determining the subject vehicle can passthrough a curve existing ahead of the subject vehicle at a currentvehicle speed V₀, based on the shape of the road searched by the coursesearching means and based on the vehicle speed V₀ of the subjectvehicle, and a control means 24 which varies the engine output or thebraking force so as to enable the subject vehicle to pass through thecurve, based on the determination by the passability/impassabilitydetermining means 23, thereby operating a vehicle speed regulating means25 for regulating the vehicle speed and/or a warning means for giving awarning for pressing the driver for a speed reduction.

The function of the cornering control section CC will be described belowwith reference to a flowchart in FIG. 19.

First, a current position P₀ (X₀, Y₀) and a vehicle speed V₀ of thesubject vehicle (at steps S21 and S22) Then, a preread distance S iscalculated based on the vehicle speed V₀ (at step S23). A temporaryposition P₁ (X₁, Y₁) of the subject vehicle is calculated from theposition P₀ (X₀, Y₀) of the subject vehicle and the preread distance S(at step S24). As shown in FIGS. 20 and 21, the temporary position P₁(X₁, Y₁) of the subject vehicle is a reference position suitable todetermine whether the subject vehicle can pass through the curve and toset a passable vehicle speed V_(MAX) at which the subject vehicle canpass through the curve, and the larger the vehicle speed V₀, the prereaddistance S is set longer, so that a sufficient speed-reducing distancecan be insured when the current vehicle speed V₀ is too large and thesubject vehicle cannot pass through a curve located ahead of thetemporary position P₁ (X₁, Y₁) of the subject vehicle.

Next, the minimum turnable radius R is map-searched based on the vehiclespeed V₀ (at step 25). The minimum turnable radius R is large when theV₀ is high, and is small when the vehicle speed V₀ is low.

Then, a passable area A is calculated. More specifically, two circulararcs C₁ and C₂ having the same radius which is the minimum turnableradius R are described in the temporary position P₁ (X₁, Y₁) of thesubject vehicle in such a manner that they are tangent to each other,and a passable area A is established outside the two circular arcs C₁and C₂ (at step S26). As shown in FIG. 26, when the vehicle speed V₀ issmaller, the minimum turnable radius R of the vehicle is smaller andhence, the passable area A is wider. Reversely, as shown in FIG. 21,when the vehicle speed V₀ is larger, the minimum turnable radius R ofthe vehicle is larger and hence, the passable area A is narrower.

Then, it is determined whether a plurality of nodes N (=N₁, N₂, N₃ --)established on a road exist within the passable area A (at step S27) .When the node N exist within the passable area A, as shown in FIG. 20,it is determined that the vehicle can pass through the curve at thecurrent vehicle speed V₀ as it is. Reversely, when the nodes N existoutside the passable area A, as shown in FIG. 21, it is determined thatthe vehicle cannot pass through the curve at the current vehicle speedV₀ as it is.

Whether the nodes N exist either inside or outside the passable area Ais determined in the following manner: If both of distances L₁ and L₂between the centers of the two circular arcs C₁ and C₂ of the radius Rand the nodes N are larger than the radius R, as shown in FIG. 22, it isdetermined that the nodes N exist inside the passable area A, and thatthe subject vehicle can pass through the nodes N at the current speedV₀. On the other hand, if one of the distances L₁ and L₂ (e.g., L₂)between the centers of the two circular arcs C₁ and C₂ of the radius Rand the nodes N is smaller than the radius R, as shown in FIG. 23, it isdetermined that the nodes N exist outside the passable area A, and thatthe subject vehicle can pass through the nodes N at the current speedV₀.

For example, even if the nodes N₁ and N₃ exist inside the passable areaA, if the node N₂ exists outside the passable area A, as shown in FIG.24, the vehicle cannot pass through the curve at a vehicle speed V₀ leftintact. Therefore, to permit the vehicle to pass through the curve atthe current vehicle speed V₀, it is required that all the nodes N existinside the passable area A.

Now, when it has been determined at step S27 that the vehicle cannotpass through the curve, a maximum turning radius R' required for thesubject vehicle to pass through the curve is calculated (at step S28).The maximum turning radius R' is set as a radius R' of circular arcs C₁' and C₂ ' as larger as all the nodes do not exist inside the circulararcs C₁ ' and C₂ ' (see FIG. 24) . Therefore, if the vehicle speed ofthe subject vehicle is reduced to a level enable the vehicle to beturned at the maximum turnable radius R', the vehicle can pass throughthe curve.

Then, the vehicle speed enabling the vehicle to be turned at the maximumturnable radius R' is determined as a passable vehicle speed V_(MAX) (atstep S29), and the vehicle speed V₀ is reduced down to a level equal toor lower than the passable vehicle speed V_(MAX) (at step S30). Thus,the vehicle can reliably pass through the curve.

If all the nodes N exist inside the passable area A, the vehicle canpass through the curve at the speed V₀ left intact and hence, the speedreduction by the vehicle speed regulating means 25 is not carried out.

In the manner, it is determined whether the vehicle can pass through thecurve. If the vehicle cannot pass through the curve at the currentspeed, the subject vehicle is enabled to pass through the curve at aproper vehicle speed by conducting a speed reduction by the warningmeans 26 and the vehicle speed regulating means 25.

The function of the follow-up travel control section FC in the tenthembodiment has the vehicle speed control substituted for the steeragecontrol in the flowchart in FIG. 16 illustrating the ninth embodiment.More specifically, when the follow-up travel control by the follow-uptravel control section FC is started while the vehicle speed control bythe cornering control section CC is being conducted in order to preventthe departing of the vehicle from the road in the curve, the vehiclespeed control is automatically discontinued. When the ahead-travelingvehicle has been lost of sight during the follow-up travel control,thereby causing the follow-up travel control to be disenabled, thevehicle speed control is automatically restarted. Thus, it is possibleto exhibit the functions of both the controls to the maximum withoutcausing the drive to feel the incompatibility and the troublesomenessdue to a mutual interference.

In the previously described ninth embodiment and the tenth embodiment,for example, a photographing or shooting means such as a camera can beemployed in place of the radar sensor S₆. As for the steerage controlsection SC, any proper one can be employed if it is adapted to perform asteerage control in accordance with the road shape detected based themap information. Further, as for the cornering control section CC, anyproper one can be employed if it is adapted to perform the regulation ofthe vehicle speed in accordance with the road shape detected based themap information.

An eleventh embodiment of the present invention shown in FIG. 25 issubstantially similar to the sixth embodiment, except that in place ofthe various sensors S₂ to S₇ connected to the control means 13 of thesteerage control section SC in the sixth embodiment, a steering angularvelocity sensor S₈ connected to the control means 13 is used. Otherconstructions are the same as in the sixth embodiment.

The operation of the eleventh embodiment will be described below withreference to a flowchart in FIG. 26. First, a position of a subjectvehicle on a map and data of a road ahead of the subject-vehicleposition are read by the navigation system NV (at step S1 and S2). Then,an azimuth change quantity θ of the road (i.e., an azimuth changequantity θ between a second node N₂ and a third node N₃) is calculatedby the above-described technique shown in FIG. 3, and a reference yawrate γ_(REF) is calculated by dividing the azimuth change quantity θ bya time δt required for the vehicle to travel from the second referencenode N₂ to the third reference node N₃ (at step S4).

Then, an actual yaw rate γ is read from the yaw rate sensor 1 (at stepS5), and a deviation D (=γ-γ_(REF)) between the reference yaw rateγ_(REF) determined at step S4 and the actual yaw rate γ determined atstep S5 (at step S6). A steerage assisting torque T (=k₁ ×D)proportional to the deviation D is determined (at step S7). If thedeviation D is positive, a steerage ssisting torque permitting thesteering control wheel to be steered rightwardly is applied to thesteering means 15, and if the deviation D is negative, a steeragessisting torque permitting the steering control wheel to be steeredleftwardly is applied to the steering means 15. (at step S8).

The operations at steps S1 to S8 are the same as those in the sixthembodiment (see FIG. 9).

Now, when the driver has found an obstacle ahead and has operated thesteering wheel in order to avoid the obstacle, as shown in FIG. 27, ifthe steering angular velocity dθ_(ST) /dt detected by the steeringangular velocity sensor 17 exceeds a reference value α, it is determinedthat the obstacle avoiding operation has been conducted (at step S9),and the steerage assisting torque T is corrected by a correctingquantity ΔT in order to assist the avoiding operation (at step S10). Thecorrecting quantity ΔT is given by a product of a constant k₂ and thesteering angular velocity dθ_(ST) /dt according to an equation, ΔT=k₂×dθ_(ST) /dt. Therefore, the steerage assisting torque T during theobstacle avoiding operation is given according to the followingequation:

    T=(k.sub.1 ×D)-(k.sub.2 ×dθ.sub.ST /dt)  (10)

which is corrected by subtracting the correcting quantity ΔT from thesteerage assisting torque T (=k₁ ×D) in a normal condition, which isproportional to the deviation D (γ-γ_(REF)) between the reference yawrate γ_(REF) and the actual yaw rate γ.

This will be further described. If the driver suddenly operates thesteering wheel rightwardly in order to avoid an obstacle found ahead,when the vehicle is traveling, for example, on a rightwardly curved roadas shown in FIG. 27, a rightward large actual yaw rate γ is generated toproduce a deviation D between such actual yaw rate γ and a reference yawrate γ_(REF) based on a curvature of the road. As a result, a leftwardsteering torque k₁ ×D is applied to the steering means 15, so that thevehicle is intended to be restored to a correct course. However, thissteering torque k₁ ×D is in a direction opposite from the direction ofsteering wheel operated by the driver to avoid the obstacle, resultingin an increased burden for driver's obstacle-avoiding operation.

Thereupon, in order to eliminate the leftward steering torque k₁ ×D andto assist the rightward steerage conducted by the driver during theobstacle avoiding operation, the steering torque k₁ ×D is corrected bythe steering torque correcting quantity k₂ ×dθ_(ST) /dL in a reversedirection from the direction of the steering torque k₁ ×D. The negativesign in the equation (5) indicates that the correcting quantity k₂×dθ_(ST) /dt acts in a direction to eliminate the steering torque k₁ ×D.Thus, it is possible to easily and properly conduct the obstacleavoiding operation without interfering with the steerage control forpreventing the departing of the vehicle from the road.

When the driver has returned the steering wheel to causes the steeringangular velocity dθ_(ST) /dt to become 0 (zero), the value of thecorrecting quantity k₂ ×dθ_(ST) /dt also becomes 0 (zero) and thus, theobstacle avoiding operation is completed (at step S11).

It is also possible to assist a steerage for permitting the vehicle tobe returned to an original travel lane with an appropriate timing afteravoidance of the obstacle. In this case, a quantity of lateral movementof the vehicle for avoiding the obstacle, shown by L in FIG. 27, ispreviously calculated based on the yaw rate and the hysteresis of thevehicle speed during the obstacle avoiding operation, or based on thevariation in current position of the vehicle by the navigation system.When the driver has operated the steering wheel or the winker in orderto return the vehicle to the original travel lane, a steering torquecorresponding to the lateral movement quantity L can be applied toassist the driver's returning operation.

A twelfth embodiment of the present invention will now be described withreference to FIGS. 28 and 29.

As shown in FIG. 28, a steerage control section SC in the twelfthembodiment includes a ahead-obstacle sensor S₉ comprised of a radarsensor for detecting an obstacle ahead of the subject vehicle, aside-obstacle sensor S₁₀ comprised of a radar sensor for detecting anobstacle existing sideways of the subject vehicle, in place of thesteering angular velocity sensor S₈ used in the eleventh embodiment.Other constructions are the same as in the eleventh embodiment.

As shown in FIG. 29, when an obstacle has been detected by theahead-obstacle sensor S₉, the size of the obstacle and the distancebetween the subject vehicle and the obstacle, as well as if the latteris moving, the relative speed of the subject vehicle relative to theobstacle, are calculated. If there is a possibility that the subjectvehicle may collide against the obstacle, the driver is informed of suchpossibility by an informing means such as a buzzer, a chime, a voice andthe like, and the avoidance assisting for avoiding the obstacle iscarried out.

The avoidance assisting is conducted by providing the correctingquantity ΔT in a direction to avoid the obstacle and correcting thesteerage assisting torque T based on the deviation D (γ-γ_(REF)) betweenthe reference yaw rate γ_(REF) and the actual yaw rate γ, as in theeleventh embodiment. In the twelfth embodiment, however, the correctingquantity ΔT is determined by the size of the obstacle detected by theahead-obstacle sensor S₉, the distance between the subject vehicle andthe obstacle and the relative speed of the subject vehicle relative tothe obstacle. Specifically, the larger the obstacle, the smaller thedistance between the subject vehicle and the obstacle and the larger therelative speed of the subject vehicle relative to the obstacle (in otherwords, the subject vehicle is rapidly approaching to the obstacle), thelarger the correcting quantity ΔT is set. This provides a reliableavoidance of the obstacle.

When the subject vehicle has reached a location sideways of the obstacleby the avoiding operation, the side-obstacle sensor S₁₀ detects theobstacle in place of the ahead-obstacle sensor S₉. At this time, thedriver is informed by an informing means such as a buzzer, a chime, avoice and the like to wait the returning of the subject vehicle to anoriginal travel lane. When it is detected that the subject vehicle hasreached a location ahead of the obstacle, the operation of the informingmeans is stopped to inform the driver the fact that the returning of thesubject vehicle to the original travel lane is possible. Even when thedriver conducts a steerage to cause the subject vehicle to return to theoriginal travel lane, the returning operation is assisted by thecorrecting quantity ΔA corresponding to the quantity L of lateralmovement of the vehicle, as in the eleventh embodiment.

Each of the ahead-obstacle sensor S₉ and the side-obstacle sensor S₁₀ isnot limited to the radar sensor and may be a photographing or shootingmeans such as a camera. The control for preventing the departing of thevehicle from the road is not limited to a control based on the deviationD between the reference yaw rate γ_(REF) and the actual yaw rate γ, anda proper control can be employed.

What is claimed is:
 1. A vehicle control system comprising:a mapinformation outputting means for outputting map information including aroad on which a subject vehicle travels; a subject-vehicle positiondetecting means for detecting a subject-vehicle position on a map; asteering means for steering a steering control wheel of the vehicle; asteering-torque applying means for applying a steering torque to saidsteering means; an ahead-obstacle detecting means for detecting anobstacle ahead of the vehicle; a side-obstacle detecting means fordetecting an obstacle sideways of the vehicle as an indication that thevehicle has avoided the obstacle; and a steerage control means fordetermining a steering-torque application quantity based on a travelingstate of the vehicle and a shape of a road ahead of the subject vehicleposition on the map to drive said steering-torque applying means, forcorrecting said steering-torque application quantity in a manner such asto avoid an obstacle ahead of the subject vehicle if such an obstacle isdetected by said ahead-obstacle detecting means, and for correcting saidsteering-torque application quantity in a manner opposite to the mannersuch as to avoid said obstacle, if said side-obstacle detecting meansdetects that the subject vehicle has avoided said obstacle.
 2. A vehiclecontrol system according to claim 1, further including alarm means forproviding a warning to a driver of the vehicle if the control meansdetermines that there is a possibility the vehicle may collide with theobstacle detected by said ahead-obstacle detecting means.
 3. A vehiclecontrol system according to claim 1, wherein said control meansdetermines a correction amount for correcting said steering-torqueapplication quantity according to at least one of a size of the obstacledetected by said ahead obstacle detecting means and a distance betweenthe vehicle and the obstacle detected by said ahead-obstacle detectingmeans.
 4. A vehicle control system according to claim 3, furtherincluding means for determining a relative speed of the vehicle relativeto an obstacle detected by said ahead-obstacle detecting means, and saidcontrol means determines said correction amount for correcting saidsteering-torque application quantity also according to a relative speeddetermined by said relative speed determining means.
 5. A vehiclecontrol system according to claim 1, further including means fordetermining a relative speed of the vehicle relative to an obstacledetected by said ahead-obstacle detecting means, and said control meansdetermines a correction amount for correcting said steering-torqueapplication quantity according to a relative speed determined by saidrelative speed determining means.
 6. A vehicle control system accordingto claim 1, further including informing means for providing anindication to a driver of the vehicle when said side-obstacle detectingmeans has detected an obstacle sideways of the vehicle.
 7. A vehiclecontrol system according to claim 6, wherein said informing meansprovides said indication to the driver until the vehicle has reached alocation ahead of the obstacle.